The present invention relates to a two-wheeled inverted robot in which coaxial two wheels are used among robots which perform load carriage work, and particularly relates to the two-wheeled inverted robot in constraining the robot attitude.
In the robot which performs the load carriage work, generally the robot maintains its stability by necessarily bringing at least three points into contact like a three-wheel type robot or a four-wheel type robot. However, the three-wheel type robot or the four-wheel type robot occupies a large area and hardly has a small turning circle. Therefore, there has been developed a coaxial two-wheel type robot which operates based on an inverted pendulum model.
For example, there is known a coaxial two-wheel type moving robot described in Japanese Patent No. 2530652 and Japanese Unexamined Patent Publication No. 2004-74814.
FIG. 13 shows a conventional coaxial two-wheel type moving robot described in Japanese Patent No. 2530652.
The coaxial two-wheel type moving robot described in Japanese Patent No. 2530652 includes a body 104, a wheel drive motor 105, a control computer 106, and an angle detection means 107. The body 104 is rotatably supported on an axle shaft 101 which includes a pair of wheels 102 and 103 at both ends. The wheel drive motor 105 is attached to the body 104. The control computer 106 issues an operation command to the wheel drive motor 105. The angle detection means 107 detects inclination of the body 104. An inclination angle of the body 104 detected by the angle detection means 107 is sampled at short time intervals, the inclination angle of the body 104 is set at a state variable input value, and a feedback gain K is set at a coefficient. Then, a control torque of the wheel drive motor 105 is computed to perform state feedback control based on a control input computation equation which is previously inputted and set in the control computer 106. The control computer 106 issues an actuation command corresponding to the computed control torque to the wheel drive motor 105, which maintains the inverted attitude control.
FIG. 14 shows a conventional human-transport coaxial two-wheel type moving robot described in Japanese Publication No. 2004-74814.
In the human-transport coaxial two-wheel type moving robot described in Japanese Publication No. 2004-74814, the attitude control and running control are performed to maintain a fore-and-aft balance by controlling and driving right and left driving wheels 202 coaxially arranged on a platform 201 according to output of an attitude sensor. The human-transport coaxial two-wheel type moving robot includes an auxiliary wheel 203 which comes into contact with the ground on the front side and/or rear side of the driving wheels 202 and an auxiliary wheel drive unit 204 which extends and retracts the auxiliary wheel 203. The human-transport coaxial two-wheel type moving robot includes a control circuit which drives the auxiliary wheel drive unit 204 to extend and retract the auxiliary wheel 203 according to an obstacle detection sensor 205 and control states of running speed and attitude. Therefore, when an obstacle which tends to cause falling exists, because the auxiliary wheel 203 is extended to enhance safety, the risk of the falling can be decreased.
In the technique described in Japanese Patent No. 2530652, the state feedback control is always performed.
When the coaxial two-wheeled body 104 and the wheels 102 and 103 can relatively be rotated with no constraint, the torque generated by the wheel drive motor 105 contributes to the rotations of the wheels 102 and 103, and simultaneously a reaction torque acts on the body 104 to be able to maintain the inverted attitude control as a whole.
However, when a part of the body 104 comes into contact with a wall or the ground to receive a constraint force from the outside to such an extent that the body 104 cannot rotate any more, not only does the body 104 not rotate, but also the torque generated by the constraint force is transmitted to the wheels 102 and 103. Therefore, when compared with no constraint force, the excessive torque is applied to the wheels 102 and 103, which results in an issue that the wheel rotation is increased to rapidly enhance the running speed.
In the technique described in Japanese Publication No. 2004-74814, when the obstacle is detected by the obstacle detection sensor 205, because the human-transport coaxial two-wheel type moving robot has the mechanism in which the auxiliary wheel drive unit 204 is driven to extend and retract the auxiliary wheel 203, the extension of the auxiliary wheel 203 enables the three-point ground contact of the right and left driving wheels 202 and the auxiliary wheel 203 to decrease the risk of falling.
However, in the technique described in Japanese Publication No. 2004-74814, only the obstacle is recognized to extend the auxiliary wheel 203, and the speed and the attitude depend on the control of a user. Therefore, in the configuration described in Japanese Publication No. 2004-74814, as with Japanese Patent No. 2530652, there is also the issue that excessive torque is applied to the driving wheel 202 to rapidly enhance the running speed, when a user breaks down the balance to bring the body portion including the platform 201 into contact with the ground, or when the body portion including the platform 201 is brought into contact with the wall or the like to receive the constraint force to such an extent that the body portion cannot rotate. In this case, a stop command is transmitted to avoid the risk by the control of the user. However, there is the issue that a burden is placed on the user to the point that the operation depends on the user.
An object of the present invention is to provide a safe two-wheeled inverted robot and a control method thereof, in which the above issues are solved and the attitude control and the running state can be maintained and the burden is not placed on the user, when a part of the body of the coaxial two-wheeled robot which is moved while the inverted control is performed comes into contact with the ground or the wall to receive the constraint force.